Mark Alen
2011-Jul-23 05:02 UTC
[R] Calculating the mean of values in tables using formulae
I know commands like xtabs and table allow a user to do cross-tabulation For example the following command generates a pivot table that shows the number of cars that have the same number of gears and cylinders.>xtabs(~cyl+gear,data =mtcars)? ?gear cyl ?3?4?5 ? 4?1?8?2 ? 6?2?4?1 ? 812?0?2>We can extend the formula so it could show the sum of the horse power for the cars in each bin>xtabs(hp~cyl+gear,data =mtcars)? ?gear cyl ? ?3? ?4? ?5 ? 4? 97?608?204 ? 6?215?466?175 ? 82330? ?0?599>I am now wondering, is it possible to calculate the mean of horse powers for cars in each bin? for example something like this?xtabs(mean(hp)~cyl+gear, data = mtcars) Thank you? Mark
Daniel Malter
2011-Jul-23 05:40 UTC
[R] Calculating the mean of values in tables using formulae
Check the *apply() series of functions. tapply() will do what you want. attach(mtcars) tapply(hp,list(cyl,gear),mean) HTH, Daniel Mark Alen wrote:> > I know commands like xtabs and table allow a user to do cross-tabulation > For example the following command generates a pivot table that shows the > number of cars that have the same number of gears and cylinders. > >>xtabs(~cyl+gear,data =mtcars) > ? ?gear > cyl ?3?4?5 > ? 4?1?8?2 > ? 6?2?4?1 > ? 812?0?2 >> > > We can extend the formula so it could show the sum of the horse power for > the cars in each bin > >>xtabs(hp~cyl+gear,data =mtcars) > ? ?gear > cyl ? ?3? ?4? ?5 > ? 4? 97?608?204 > ? 6?215?466?175 > ? 82330? ?0?599 >> > > I am now wondering, is it possible to calculate the mean of horse powers > for cars in each bin? for example something like > this?xtabs(mean(hp)~cyl+gear, data = mtcars) > > Thank you? > Mark > > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >-- View this message in context: http://r.789695.n4.nabble.com/Calculating-the-mean-of-values-in-tables-using-formulae-tp3688416p3688437.html Sent from the R help mailing list archive at Nabble.com.